Different techniques are known for three dimensional imaging.
It is known to carry out three dimensional particle imaging with a single camera. This is also called quantitative volume imaging. One technique, described by Willert and Gharib uses a special defocusing mask relative to the camera lens. This mask is used to generate multiple images from each scattering site on the item to be imaged. This site can include particles, bubbles or any other optically-identifiable image feature. The images are then focused onto an image sensor e.g. a charge coupled device, CCD. This system allows accurately, three dimensionally determining the position and size of the scattering centers.
Another technique is called aperture coded imaging. This technique uses off-axis apertures to measure the depth and location of a scattering site. The shifts in the images caused by these off-axis apertures are monitored, to determine the three-dimensional position of the site or sites.
U.S. Pat. No. 7,006,132 describes a geometric analysis in which a camera lens of focal length f is located at z=0. Two small apertures are placed within the lens, separated a distance d/2 away from the optical centerline which also corresponds to the z axis.
U.S. Pat. No. 7,006,132 describes using lens laws and self similar triangle analysis to find the geometrical center (X0,Y0) of the image pair, and then to solve for the image separation.
More generally, this can determine the pose of a camera that is obtaining the information, and the information from the camera, to determine 3D information about structures that is pieced together from multiple different images. US 2009/0295908 describes how camera pose can be simultaneously measured by using an additional set of apertures that measure a pose of the camera relative to the object when using a feature matching algorithm, using the same apertures that are used for defocusing.
There are often tradeoffs in aperture coding systems.